Research Article Cite This: ACS Sustainable Chem. Eng. XXXX, XXX, XXX−XXX
Corn Stalk Fiber-Based Biomass Brick Reinforced by Compact Organic/Inorganic Calcification Composites Chao Ma,†,⊥ Shuai Zhang,‡,⊥ Rongdan Dong,† Meng Wang,§ Wanda Jia,† and Zeguang Lu*,† †
College of Forestry, Shandong Agricultural University, Taian 271018, Shandong, China College of Chemistry and Material Science, Shandong Agricultural University, Taian 271018, Shandong, China § College of Water Conservancy and Civil Engineering, Shandong Agricultural University, Taian 271018, Shandong, China ‡
ABSTRACT: Biomass brick is green, reproducible and environment-friendly material with broad market prospects. In this work, corn stalk fiber-based biomass bricks are molded with calcium hydroxide (Ca(OH)2) as the adhesive in order to increase the strength of bricks. Because of the strong basicity of Ca(OH)2, corn stalk fiber was partially, incompletely degraded during the process of cold press and hot air drying, resulting in the formation of compact organic/inorganic composites. The hydrogen bond between cellulose and hemicellulose is weakened, the ester bond between hemicellulose and lignin is saponified, and the ether bond of lignin is broken, resulting in that the structure of fiber is destroyed, and facilitating the generation of organic/inorganic composites. The results of a series of tests, including scanning electron microscopy, X-ray diffraction, infrared spectroscopy, nuclear magnetic resonance and so on, confirmed a desired change in structure of the fibers and the formation of composites. Furthermore, this composite structure significantly improved the strength of the brick. KEYWORDS: Biomass brick, Corn stalk fiber, Calcium hydroxide, Structure, Calcium ion
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INTRODUCTION There is about 1.0 billion tons corn stalk in the world and 0.25 billion tons in China.1,2 Resource and industrialization utilization of stalk is a fundamental policy for solving the problems about stalk waste and burning.3−5 There is about 40 billion m2 in building area in China now,6 and the area will be 68.6 billion m2 by 2020.7 The introduction of stalk into the architecture industry can accomplish the merger development of the two industries, which solves the problem about the serious resource and energy and environmental pressure, and explores a new way for the agricultural economy.3,8,9 Corn stalk fiber can be manufactured into corrugated paper,10 packaging material,11 foamed material,12 straw− cement composite material, straw−plastic composite material, straw−wood composite material,3 and heat insulating material.13 Calcium hydroxide (Ca(OH)2) is an inorganic binder as the earliest adhesive in history,14 which has a good flameretardant property.15 It can be manufactured into calcium hydroxide slurry,16 cement mortar,17 tung oil mortar,18 and sticky rice mortar,19 used widely in architecture engineering. Therefore, it is reasonable that corn stalk fiber and calcium hydroxide can be molded into the lightweight biomass brick for building indoor partitions. Biomass brick is green, reproducible, and environmentfriendly material. It is similar to wood, which has good sense of touch, warmth, and decor. It can balance the relative humidity of indoor air, improve the indoor environmental quality, and increase the housing habitability with the characters of moisture desorption and absorption. It conforms to the trend of lightweight development of wall materials.7 © XXXX American Chemical Society
The brick belongs to the new architecture material with broad market prospects. However, no studies have been done on the synthesis mechanisms of corn stalk fiber and calcium hydroxide to strengthen the bricks. The purpose of this study is to obtain useful information about the mechanisms using scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction analysis (XRD), solid state nuclear magnetic resonance (SSNMR), thermogravimetric analysis (TG), and differential scanning calorimetry (DSC).
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EXPERIMENTAL SECTION
Materials. Properties of corn stalk fiber (Shandong Province, China) and Ca(OH)2 (Shandong Province, China) are shown in Tables 1 and 2. Methods. Technology roadmap is shown in Figure 1. The mass of corn stalk fiber and Ca(OH)2 are weighed using an electrical balance (Model JA21002, Shanghai Jingtian Electrical Instrument Co., Shanghai, China) with a precision of 0.01 g. The mass of corn stalk
Table 1. Moisture Content and Density of Raw Materials Corn stalk fiber
Ca(OH)2
Raw materials
Range
Mean
Range
Mean
Moisture content (%) Density (g/cm3)
10.05 to 10.76 0.100 to 0.104
10.29 0.103
47.36 to 52.20 1.015 to 1.115
49.63 1.070
Received: September 29, 2017 Revised: November 25, 2017 Published: December 14, 2017 A
DOI: 10.1021/acssuschemeng.7b03509 ACS Sustainable Chem. Eng. XXXX, XXX, XXX−XXX
Research Article
ACS Sustainable Chemistry & Engineering Table 2. Mass Ratio of Corn Stalk Fiber Mesh (number) Mass percent (%)
10 0.15
20 11.92
30 19.32
40 18.32
50 15.80
60 7.61
70 3.99
80 5.21
90 1.50
100 2.37
≥100 13.81
Huibo Industry and Trade Co., Shenzhen, China) with the precision of 0.01 s. The wet brick is dried for 48 h in the hot air drying house (Model 4.5 m × 2.8 m × 3.0 m (length and width and height), Jinan Longxiang Painting Equipment Co., Jinan, China), where it is 60 °C in air temperature, 30.1% in air relative humidity, and 0.20 m/s in air velocity. The heating rate is 1.2 °C/min and the precision is 0.1 °C. Air relative humidity and temperature are measured using a temperature humidification electrical meter (Model 310 RS-232, Center Technology Co., Taiwan, China), and the velocity is measured using a thermo ball electrical wind velocity meter (Model QDF-3, Inspection Equipment Co., Beijing, China). The dimensions of the dry brick in length, width and thickness are measured with the plastic ruler (Model 30 CM, Deli Group Co., Zhejiang, China). Its mass is weighed with an electrical balance (Model ACS-302, Shanghai Huachao Electrical Instrument Co., Shanghai, China) with a precision of 1 g. When the brick is dried after 48 h, the dimensions of the brick are equal to 235 mm in length, 110 mm in width, and 55 mm in thickness. Moisture content is equal to 15.61%. When the drying process is over, compression strength of the dry brick is tested immediately. Compression strength of the dry brick is tested with an electrical strength test machine (Model DTH-300B, Shandong Luda Test Measurement Machine Co., Taian, China). The brick is loaded vertically in thickness at 1.0 mm/min movement velocity. When the deformation reaches 2.5 mm in thickness, the load is the compression strength. The thickness of the brick is as same as before when the press is unloaded. It takes 2.5 min to finish the test. The test process is shown in Figure 2.
Figure 1. Technology roadmap. Figure 2. Test process of compression strength.
fiber is 327.13 g and that of Ca(OH)2 is 1864.15 g. They are mixed completely with a mixing machine (Model JJ-5, Shandong Luda Test Measurement Machine Co., Taian, China) and put into squeeze die. The squeeze die is customized for the experiment (Model Custom, Shandong Luda Test Measurement Machine Co., Taian, China). The die consists of a squeeze head, a bucket and a backing board. The head is the loading body. The bucket has a rectangular shape, and its interior dimensions are 235 mm in length, 110 mm in width and 150 mm in thickness. The backing board is the loaded body. The brick is molded in the cold press machine (Model MY 50B, Qingdao Jilongchang Equipment Machine Co., Qingdao, China). The pressure is 10 MPa when the head is pressed into the bucket completely. The pressing is maintained for 10 min (press time), and the temperature is 12.4 °C (room temperature). The temperature is decided by the air temperature when the brick is molded. The press time is measured with a second meter (Model PC 396, Shenzhen
Micromorphologies about corn stalk fiber, Ca(OH)2, and brick are observed with scanning electron microscopy (SEM), (Model JSM 7800F, Jeol Co., Shunsuke Asahina, Japan). Fourier transform infrared spectrum (FTIR) is used to measure the change of functional groups (Model TENSOR27, German Bruker Co., Karlsruhe, Germany). The crystalline structures are characterized by X-ray diffraction (Model D8 ADVANCE, German Bruker Co., Karlsruhe, Germany). NMR spectra are examined with solid state nuclear magnetic resonance (SSNMR, Model Agilent 600 MHz DD2, Agilent Technologies Co., Palo Alto, America). Thermal stability and composition are investigated with thermogravimetric analysis (TG, Model Q600, TA Instruments Co., New Castle, USA). Temperature ranges from 25 to 800 °C in the N2 environment, the heating rate is equal to 20 °C/min. Thermodynamics characters are discussed with differential scanning calorimetry B
DOI: 10.1021/acssuschemeng.7b03509 ACS Sustainable Chem. Eng. XXXX, XXX, XXX−XXX
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exchanges, and to inhibit combustion.23,24 Therefore, the brick has flame retardant property.
(DSC, Model Q100, TA Instruments Co., New Castle, USA). Temperature ranges from 0 to 400 °C in the N2 environment, the heating rate is 5 °C/min. The brick is dried to absolute dryness (0% moisture content) via a hot air drying box (Model DUG 9123A, Shanghai Jinghong Experiment Instrument Co., Shanghai, China) with the precision of 0.1 °C, where the hot air temperature is 100 °C. The mass of the dried brick is tested using an electrical balance (Model JA21002, Shanghai Jingtian Electrical Instrument Co., Shanghai, China) with a precision of 0.01 g.
Ca(OH)2 → Ca 2 + + 2OH−
(1)
A corn stalk fiber brick is molded from loose, big volume to a compact and small solid one.6 Ca(OH)2 is a continuous phase and corn stalk fiber is a dispersed one. The mixture is squeezed to shorten the interspaces of fibers and increase the contact surface. During the process of cold press, Ca(OH)2 particles are localized on the internal and external surfaces of cellulose and lignin of fibers due to formation of primary metal complexes between Ca2+ ions with OH functional groups from the cellulose and lignin via hydrogen bonding. The placement of Ca(OH)2 in the internal spaces of fibers (pores and their internal surfaces) and external surfaces cause an increased interaction between fiber and Ca(OH)2. During the process of hot air drying, in the strong alkaline environment (pH = 12.4) of Ca(OH)2, the hydrogen bond between cellulose and hemicellulose is weakened, the ester bond between hemicellulose and lignin is saponified, and the ether bond of lignin is broken, as illustrated in Figure 4. As a result, lignin and
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RESULTS AND DISCUSSION Studies on Micromorphologies about Corn Stalk Fiber, Ca(OH)2, and Brick. After corn stalk fiber and Ca(OH)2 are molded into the brick, their micromorphologies are changed significantly, as shown in Figure 3a,b. Corn stalk
Figure 4. Synthetic mechanism about corn stalk fiber brick. Figure 3. SEM characterizations about corn stalk fiber, Ca(OH)2, and brick.
hemicellulose are dissolved in Ca(OH)2, cellulose swells, and the crystallization index of cellulose decreases.20 Figure 3e,f shows the images of the brick and reveal the significant changes in fibers. No corn stalk fiber raw material is observed in the brick SEM, as shown in Figure 3e,f. After the process of cold press and hot air drying completed, corn stalk fiber was partially, incompletely degraded by reacting with Ca(OH)2, and provided amount of insoluble calcification. Finally, the compact organic/inorganic composite structure is constructed to increase the strength of the brick. In the composite, there are hydrogen bond, van der Waals’ force, pastern nail, interwoven friction, and chemical bond,25 which contributed to the structure and properties of the brick. Furthermore, during the hot drying process, Ca(OH)2 reacts with carbon dioxide (CO2), released from the heated fiber, to generate calcium carbonate (CaCO3), which increases the strength of the brick.26−32 Moisture content of the corn stalk fiber brick is
fiber as thin film, consists of 38% cellulose, 22% hemicellulose, and 18% lignin, respectively.20 There are a lot of cell cavities and cell walls in the fiber with huge surface areas, which are beneficial to promote the interaction between fiber and Ca(OH)2. Ca(OH)2 raw material piles together loosely and disorderly, as shown in Figure 3c,d. Ca(OH)2 is easily ionized to generate Ca2+ and OH− ions with pH value of 12.4 (Equation 1). What is more, Ca(OH)2 can dissolve cell membrane of bacteria in the strong alkaline environment, thus inhibits and sterilizes bacteria.21,22 Therefore, the brick has an antiseptic function. When Ca(OH)2 is burned, it undergoes carbonation reaction to form a tight carbonate barrier, to hinder the heat and mass C
DOI: 10.1021/acssuschemeng.7b03509 ACS Sustainable Chem. Eng. XXXX, XXX, XXX−XXX
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ACS Sustainable Chemistry & Engineering 15.61%, with density being 1.00 g/cm3 and compression strength being 0.39 MPa. Studies on Functional Groups about Corn Stalk Fiber, Calcium Hydroxide, and Brick. The broad absorption peaks at 3444 cm−1 in corn stalk fiber correspond to the hydroxyl (OH) stretching vibration of H2O (residual free water, physically absorbed water and crystal water) and fiber, as shown in Figure 5. Peaks at 2926, 1740, 1640, and
Figure 6. XRD patterns of corn stalk fiber, calcium hydroxide and brick.
What is more, the relative crystallinity of corn stalk fiber is calculated to be 0.69. As shown in the Figure 6, the strong and sharp diffraction peaks indicated good crystallizations of Ca(OH)2 (P3̅m1). Peaks at 2θ of 29.5°, 37.9°, 39.6°, and 43.1° match well with those of calcite CaCO3, proving that a small amount of Ca(OH)2 raw material reacts with CO2 to generate CaCO3, as shown in Equation 2.
Figure 5. FTIR spectroscopy characterizations about corn stalk fiber, calcium hydroxide, and brick.
1512 cm−1 belong to the characteristic ones of stretching vibration of CH bond in the saturated hydrocarbons, the −CO stretching vibration of ester group, the flexural vibration of OH in H2O and fibers, the characteristic vibration of the aromatic ring skeleton of lignin, respectively. The broad absorption peak at 1060 cm−1 belongs to the stretching vibration of the CO bond (ether bond in lignin, glycosidic bond in cellulose and so on). In the IR spectrum of Ca(OH)2, peaks at 3643 and 872 cm−1 belong to the characteristic vibration of the OH and CaOH bond, respectively, as shown in Figure 5. The peaks at 1428 and 1640 cm−1 are the flexural vibration absorption peaks of OH bond in moisture and Ca(OH)2 raw materials, respectively. The IR spectrum of the brick is different from those of corn stalk fiber and Ca(OH)2 (Figure 5). The characteristic absorption peaks at 872 and 3643 cm−1 decrease dramatically, thus suggesting that a large amount of Ca(OH)2 is consumed. What is more, the obvious weakening of the signal peaks at 1060 cm−1 (ether bond, CO bond) and 1740 cm−1 (lignin acyl group, CO bond) of lignin is accompanied by the increase peak at 1380 cm−1. These results inform that under the strong alkaline environment of Ca(OH)2, the ester bond between hemicellulose and lignin is saponified, the ether bond of lignin is cleaved with its number reduction. As a result, the fiber is partially degraded by Ca(OH)2, especially the lignin, leading to the weakened absorption peak of the lignin in fiber. That is, the compact organic/inorganic calcification composite is generated. Studies on X-ray Diffraction Patterns of Corn Stalk Fiber, Calcium Hydroxide, and Brick. Cellulose consists of ordered crystalline zones and irregular amorphous regions as shown in the XRD patterns of corn stalk fiber (Figure 6). Peaks at 2θ of 15.4°, 22.1°, 34.4° could be indexed to the crystal faces of (101), (002), (040) in cellulose, respectively.
Ca(OH)2 + CO2 → CaCO3 + H 2O
(2)
After Ca(OH)2 was molded into the brick, the crystal planes of Ca(OH)2 in both graphs are almost the same except the increased peak width at half height (Figure 6). It indicates that the amount of Ca(OH)2 remains in the brick, although some are consumed to generate amorphous calcification compounds. On the other hand, the crystal faces of cellulose disappear in the XRD patterns of biomass brick. It provides further support that fiber is partially degraded, and the structure of fiber is destroyed by the strong alkaline Ca(OH)2. The calcification compound is crystallized on the exposed cellulose surfaces so that no crystal faces of cellulose are observed in XRD patterns of brick. Furthermore, the crystal faces of CaCO3 also disappear, probably because that CaCO3 is wrapped in the organic/inorganic calcification composites, and cannot be subjected to X-ray diffraction. Studies on Functional Groups about Corn Stalk Fiber and Brick. Figure 7 shows the 13C SSNMR spectra of corn stalk fiber and brick. Peaks in sections of δ 60 to 110 ppm belong to cellulose. The peak at δ 63 ppm corresponds to the C6 atom of cellulose D-glucopyranose. Peaks at δ 104, 73, and 88 ppm are attributed to C1, C2,3,5, and C4 atoms in glucopyranose ring, respectively. And peaks at δ 40−32 ppm are mainly indexed to the carbon atoms of side alkyl chain in lignin. In the 13C NMR spectrum of fiber, the peak at δ 115 ppm corresponds to the ester groups, which connect hemicellulose and lignin tightly. However, its disappearance in brick proves that Ca(OH)2 is capable of saponification of ester bond. Furthermore, Ca(OH)2 can break the ether bond of lignin, so that the characteristic peak at δ 52 ppm is weakened, which belongs to the aryl methoxyl carbon of lignin. At the same D
DOI: 10.1021/acssuschemeng.7b03509 ACS Sustainable Chem. Eng. XXXX, XXX, XXX−XXX
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ACS Sustainable Chemistry & Engineering
Figure 7. SSNMR characterizations about corn stalk fiber and brick.
time, peaks at δ 40, 33, and 24 ppm, corresponding to alkane group, are obviously enhanced. Studies on Thermal Stability and Composition about Corn Stalk Fiber, Calcium Hydroxide, and Brick. The TG curve of corn stalk fiber includes three weightloss segments, as shown in Figure 8a. There is 13.4% weightloss in the first segment from room temperature to 100 °C. It is attributed to the evaporation of residual water, physical adsorption water and crystalline water in the fiber. At 65 °C, the maximum dehydration rate of fiber reached up to 0.30%/°C. A platform with no weight loss is obtained in the range of 100 to 200 °C, because the moisture of fiber has been evaporated completely and no pyrolysis of fiber happens. With the increasing temperature, thermal degradation of fiber takes place gradually. There is 51.3% weightloss in the second segment from 200 to 350 °C, which is the most significant range of thermal decomposition. Under this heat condition, glucosyl and glycosidic bonds are cleaved dramatically. Small molecule gases including carbon monoxide, CO2 and methane are released. The TG curve decreases rapidly and the weightloss rate increases gradually. At 323 °C, the weightloss rate of the fiber reaches the maximum value of 0.66%/°C. Subsequently, the deep thermal degradation of fiber happens with 37.3% weightloss from 350 to 675 °C, the further pyrolysis of the residue materials continues. Therefore, the thermal decomposition rate declines and the weightloss rate decreases. When the temperature is more than 675 °C, the TG curve shows a platform state, and the weightloss is not obvious, suggesting the thermal decomposition process is over. The TG curve of Ca(OH)2 also includes three weightloss segments (Figure 8b). There is 30.0% weightloss in the first segment from room temperature to 100 °C. The water in Ca(OH)2 is evaporated rapidly by heating. At 73 °C, the weightloss rate reaches a maximum value of 0.78%/°C. The TG curve presents a platform state from 100 to 350 °C. Subsequently, in the range of 350 to 600 °C, 12.6% weightloss is observed as the second segment. When the temperature increases to 350 °C, Ca(OH)2 decomposes rapidly to generate calcium oxide (CaO) and H2O (shown in Equation 3). At 458 °C, the weightloss rate reaches 0.23%/°C. Finally, 2.7% weightloss is obtained in the third segment from 600 to 800 °C. Ca(OH)2 raw material has reacted with CO2 in the atmosphere to generate CaCO3 before molded in brick, as shown in Equation 2. Therefore, this segment is the decompose process of CaCO3, which generates CaO and CO2, as shown in Equation 4.
Figure 8. TG characterizations about corn stalk fiber, calcium hydroxide, and brick.
Ca(OH)2 → CaO + H 2O
(3)
CaCO3 → CaO + CO2
(4)
The TG curve of the brick is the result of superposition and interaction of corn stalk fiber and Ca(OH)2, including five weightloss segments and one weight increment segment (Figure 8c). 8.4% weightloss appears in the first segment from room temperature to 100 °C, in which the moisture in the fiber and calcium hydroxide is evaporated together. 2.34% weightloss is observed in the second segment from 100 to 200 °C, and the mass of the brick decreases obviously. It should be pointed out that raw materials corn stalk and Ca(OH)2 do not E
DOI: 10.1021/acssuschemeng.7b03509 ACS Sustainable Chem. Eng. XXXX, XXX, XXX−XXX
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ACS Sustainable Chemistry & Engineering appear weightloss in this segment. It indicates that fiber is apt to partial decomposition in brick and the initial temperature of degradation occurs in advance, because Ca(OH)2 can break the ether bond of lignin, saponify the ester bond between hemicellulose and lignin. There is 5.4% weightloss in the third segment from 200 to 420 °C. When the temperature is increased up to 200 °C, fiber begins to be thermally degraded rapidly. Glucosyl and glycosidic bonds are broken, and some gases including carbon monoxide, CO2 and methane are released. CO2 originates from the cleavage of the terminal group of acetyl and carboxyl groups in the hemicellulose and cellulose, and the cleavage of lateral chain carboxyl group and carbonyl group and esters in the lignin. Simultaneously, Ca(OH)2 reacts with the released CO2 to generate CaCO3 and H2O, as shown in Equation 2. Subsequently, 7.7% weightloss is found in the fourth segment from 420 to 560 °C. When the temperature rises to 420 °C, further pyrolysis of the residue of fiber continues to release CO2, water and so on. At the same time, Ca(OH)2 decomposes into CaO and water. At 436 °C, the weightloss rate reaches 0.31%/ °C. When the temperature rises up to 450 °C, the decomposition process of Ca(OH)2 finishes. Unexpectedly, there is a weight increment phenomenon (2.0%). The phenomenon is caused by the reaction of CaO and CO 2 , which has been released from the decomposition of fiber, to generate CaCO3 and lead to the mass increment, as shown in Equation 5. Finally, there is 21.4% weightloss in the fifth segment from 560 to 750 °C, which belongs to the decomposition process of CaCO3, as shown in Equation 4. At 698 °C, the decomposition rate of CaCO3 is the fastest, and the weightloss rate reaches up to 0.28%/°C. When the temperature is increased more than 720 °C, the decomposition process of CaCO3 is finished and the TG curve reaches a platform. CaO + CO2 → CaCO3
(5)
Studies on Thermodynamics Characters about Corn Stalk Fiber, Calcium Hydroxide, and Brick. DSC characterization about corn stalk fiber is shown in Figure 9a. A broad heat flow peak is illustrated from room temperature to 150 °C, corresponding to the volatilization of free water, absorbed water, and crystalline water in corn stalk fiber. At 87.6 °C, the heat flow arises to the highest and the heat effect value is 304.7 J·g−1. The second heat flow peak appears in the temperature segment from 150 to 350 °C. In this temperature stage, thermal decomposition of corn stalk fiber gradually occurs, and the glucosyl and glycosidic bonds begin to break. Interestingly, in the third temperature segment from 350 to 400 °C, the corn fiber degrades drastically, and plenty of heat is released rapidly so that this process turns to be exothermic. DSC characterization about Ca(OH)2 is shown in Figure 9b. A strong and sharp heat flow peak is displayed with heat effect value of 309.9 J·g−1. This endothermic region corresponds to the loss of a large amount of crystalline water in Ca(OH)2 hydrate, which takes place rapidly at about 100 °C. when the temperature increases up to 370 °C, Ca(OH)2 decomposes to generate CaO and H2O (Equation 3), which is illustrated as the second endothermic process. DSC characterization about the brick is shown in Figure 9c. First, the strong endothermic peak of the corn stalk fiber at 87.6 °C disappears, indicating that the moisture of the fiber in the brick basically disappears. What is more, the endothermic peak of the brick at 106.5 °C is similar to that of Ca(OH)2 at 103.7 °C, suggesting that the remained H2O exists mainly as
Figure 9. DSC characterizations about corn stalk fiber, calcium hydroxide, and brick.
crystalline water of Ca(OH)2. During the drying process, fiber is partially degraded by the alkaline Ca(OH)2, and the compact organic/inorganic calcification is generated. When the brick is heated again, fiber and calcification continue to degrade and pyrolysis rapidly, resulting in the formation of the second endothermic peak at 118 °C. In the temperature range from 150 to 350 °C, fiber continues to absorb heat and undergoes thermal decomposition reactions. When the temperature increases to 350 °C, a stronger endothermic phenomenon appears, and Ca(OH)2 decomposes into CaO F
DOI: 10.1021/acssuschemeng.7b03509 ACS Sustainable Chem. Eng. XXXX, XXX, XXX−XXX
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and H2O as shown in Equation 3. Compared to the DSC curve of Ca(OH)2, the initial temperature of the endothermic peak for the brick is 20 °C lower than that of Ca(OH)2 (370 to 350 °C). It proves that except Ca(OH)2 in the brick, new organic/ inorganic calcification compound exits, which has a lower decomposition temperature than that of Ca(OH)2.
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CONCLUSIONS A kind of corn stalk fiber-based biomass brick is molded with Ca(OH) 2 as the adhesive. A series of experimental investigation, including SEM, XRD, FTIR, SSNMR, TG, DSC tests, are carried out, providing great insight into the mechanism of these biomass bricks. During the process of cold press and hot air drying, Ca(OH)2 are located on the internal and external surfaces of fibers, the strong alkaline Ca(OH)2 can weaken the hydrogen bond between cellulose and hemicellulose, saponify the ester bonds between hemicellulose and lignin, break the ether bond of lignin. As a result, corn stalk fiber is partially degraded, with the formation of compact organic/inorganic composites, which significantly build the strength of brick. We hope this work can provide useful mechanistic information on the brick’s preparation and pave a way in the continuous development of biomass brick.
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AUTHOR INFORMATION
Corresponding Author
*Zeguang Lu, e-mail:
[email protected]. ORCID
Zeguang Lu: 0000-0002-8543-2317 Author Contributions ⊥
These authors contribute equally to this work, Chao Ma and Shuai Zhang are cofirst authors.
Author Contributions
Chao Ma manufactured the brick and performed the relative tests; Shuai Zhang analyzed data and wrote the paper; Rongdan Dong manufactured the brick and samples; Meng Wang analyzed data and discussed the paper; Wanda Jia manufactured the brick and samples; Zeguang Lu designed the research and wrote the paper. Funding
The work is supported by the Project of Special Fund for Forest Scientific Research in the Public Welfare, No. 201504506, China. Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS Engineer Eriyang in Shanghai Chenmai Technology Co., Ltd. is thanked for his help with the relative tests for the paper . REFERENCES
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DOI: 10.1021/acssuschemeng.7b03509 ACS Sustainable Chem. Eng. XXXX, XXX, XXX−XXX
